The invention is directed to a layer stack for the acceptance of a liquid, which stack has a suction layer, a storage layer and an intermediate layer.
Layer stacks of the species initially cited are known from electrolytic capacitors whereby the intermediate layer is fashioned as an anode layer, and whereby a respective suction and a storage layer are arranged at both sides of the intermediate layer. The two outermost layers of the layer stack defined in this way are respectively covered by a cathode foil. The suction or, respectively, storage layers are typically implemented as paper layers, whereby the suction layer is a paper with low density ( less than 0.6 g per cm3) and the storage layer is a paper having high density ( greater than 0.6 g per cm3). The paper layers are saturated with an electrolyte. They therefore serve, first, as storage medium for the electrolyte. Second, the paper layers also have the job of limiting the current of the mobile ions present in the electrolyte and thus achieving a high dielectric strength of the electrolytic capacitor. The electrolytic capacitors are typically manufactured by winding the above-described layer stack onto a winding mandrel, as a result whereof a cylindrical body arises. Particularly given electrolytic capacitors with high capacitance ( greater than 1 mF), cylinders having a length of a few centimeters are formed. The electrolyte is introduced into the capacitor after the winding of the capacitor. Due to the wound structure, the electrolyte can only be supplied from the end faces of the wound capacitor. Given electrolytic capacitors that exceed a specific length, the suction layer is required in order to transport the electrolyte from,the end faces into the inside. Since the suction layer is a low-density paper and has great channels, it is not suitable for achieving a high dielectric strength. The storage layer implemented as high-density paper is therefore additionally inserted between anode foil and cathode foil. The dense paper comprises channels with a small cross-section and is thus extremely well suited for achieving a high dielectric strength. Due to its low absorbency, however, the dense paper does not suffice as a sole intermediate layer between cathode foil and anode foil. The various layers described given the known structure lead to a high volume requirement of the electrolytic capacitor relative to its capacitance. Particularly where electrolytic capacitors are to be built into miniaturized circuits, this is a considerable disadvantage.
An object of the present invention is therefore to offer a layer stack that, by foregoing one of the two suction layers, comprises a lower volume requirement.
This goal or object is inventively achieved by a layer stack for the acceptance of a liquid that comprises a suction layer, a storage layer, an intermediate layer and an edge or boundary layer. The suction layer has a high absorbency sufficing for sucking up the liquid from the edge of the layer stack into a middle of the stack. The first storage layer has a low absorbency that is not sufficient for sucking up the liquid from the edge of the layer stack up to the middle. An intermediate layer adjoining the storage layer is arranged between the storage layer and the suction layer. The intermediate layer is composed of a non-absorbent material and comprises through holes. These holes connect the upper or one side of the intermediate layer to the other side or underside and are selected such in terms of plurality, size and distribution that some of the liquid suctioned up by the suction layer that is applied at the edge of the layer stack can proceed via the holes of the intermediate layers to the first storage layer and thoroughly saturate this first storage layer. A non-absorbent edge or boundary layer is arranged at that side of the first storage layer facing away from the intermediate layer. The storage layer is thus saturated with liquid exclusively via the holes in the intermediate layer.
The inventive layer stack has the advantage that a second suction layer arranged at the side of the storage layer can be eliminated by utilizing the holes found in the immediate layer for saturating the storage layer arranged at that side of the intermediate layer facing away from the suction layer. As a result thereof, the volume requirement of the layer stack is reduced.
The inventive layer stack can be especially advantageously fashioned as an electrolytic capacitor. To that end, a second storage layer is arranged at the side of the suction layer. Either the second storage layer or the suction layer can be adjacent the intermediate layer, since a good soaking of the first storage layer is achieved in both instances. The boundary or outer layer is fashioned as a first cathode layer. A second cathode layer is arranged at that side of the layer stack lying opposite the first outer layer or cathode layer. When an electrolyte, i.e., for example, an organic liquid, which has ions that conduct the electrical current is also employed, then the inventive layer stack can be employed as an electrolytic capacitor. An electrolytic capacitor designed in this way is especially space-saving due to the elimination of a second suction layer.
Paper layers are especially advantageously utilized as the suction or, respectively, storage layer. These paper layers are simultaneously suitable for the electrical insulation between the anode layer and the cathode layer and for the limitation of the ion current. The ion current is inhibited all the more greatly the thicker the paper layer between the cathode layer and the anode layer is. A paper having a density xcfx811 less than 0.6 g per cm3 is employed as the suction layer. A paper having such a low density comprises a multitude of channels that can suck a liquid applied at the edge of the layer stack into the inside as a result of capillary action. A paper having a density xcfx812 greater than 0.6 g per cm3 is preferably employed as the storage layer. Papers having this high density comprise only small channels that are especially suited for limiting the ion current in the electrolyte and, thus, for contributing to a high dielectric strength of the electrolytic capacitor.
Further, it is especially advantageous to employ a paper as the suction layer wherein a line or wave structure is impressed. A paper provided with a wave structure can, for example, look like a corrugated sheet. As a result of the impressed lines or, respectively, waves, the absorbency of the paper is enhanced, whereby the internal structure is largely preserved. A paper having a high density xcfx812 greater than 0.6 g per cm3 can therefore be employed. Such a paper then has the advantage that, on the one hand, it is suited as the suction layer and, on the other hand, comprises an enhanced dielectric strength, as a result whereof the thickness of the storage layer can be reduced.
Moreover, a layer stack is especially advantageous wherein the suction layer and the second storage layer are the plies of a two-ply paper. Such a two-ply paper can, in particular, be advantageously employed when the layer stack is wound on a winding mandrel. The two-ply paper has the advantage that it is does not tear as readily. An electrolytic capacitor manufactured of a layer stack wound onto a winding mandrel can be realized especially easily and quickly. Moreover, its capacitance can be very easily set by means of the plurality of the turns. The employment of a two-ply paper in band form for winding onto a winding mandrel is especially advantageous because only one band then need be supplied for the paper layer between anode foil and cathode foil.